EVIDENCE THAT PROTEIN-KINASE C-EPSILON MEDIATES PHORBOL ESTER INHIBITION OF CALPHOSTIN C-INDUCED AND TUMOR NECROSIS FACTOR-ALPHA-INDUCED APOPTOSIS IN U937 HISTIOCYTIC LYMPHOMA-CELLS

Protein kinase C (PKC) activators, such as the tumor-promoting phorbol esters, have been reported to protect several cell lines from apoptos is induced by a variety of agents. Recent evidence suggests that PKC e psilon is involved in protection of cardiac myocytes from hypoxia-indu ced cell death (Gray, M. O., Karliner, J. S., and Mochly-Rosen, D. (19 97) J. Biol. Chem. 272, 30945-30951). We investigated the protective e ffects of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) on U937 histiocytic lymphoma cells induced to undergo apoptosis by tu mor necrosis factor-alpha (TNF-alpha) or by the specific PKC inhibitor calphostin C. U937 cells were transiently permeabilized with a peptid e (epsilon V1-2) derived from the V1 region of PKC epsilon that has be en reported to specifically block translocation of PKC epsilon. The ep silon V1-2 peptide blocked the inhibitory effect of TPA on both TNF-al pha- and calphostin C-induced apoptosis, A scrambled version of epsilo n V1-2 and a peptide reported to inhibit PKC beta translocation (beta C2-4) had no effect on the ability of TPA to inhibit apoptosis, These results suggest that PKC epsilon is required for the protective effect of TPA in TNF-alpha- and calphostin C-induced apoptosis, Furthermore, calphostin C reduced membrane-associated PKC epsilon activity and imm unoreactivity, suggesting that PKC epsilon may play an important role in leukemic cell survival.